Semisubmerged self-clearing propeller



p 6, 1969 J. B. HADLER 3,467,052

SEMISUBMERGED SELF-CLEARING PROPELLER Filed D90. 26, 1967 JACQUES B. HADLER W AGENT ATTORNEY United States Patent Ofiice 3,467,052 Patented Sept. 16, 1969 3,467,052 SEMISUBMERGED SELF-CLEARING PROPELLER Jacques B. Hadler, Montgomery County, Md., assignor to the United States of America as represented by the Secretary of the Navy Filed Dec. 26, 1967, Ser. No. 693,395 Int. Cl. B63h 5/06 US. Cl. 115-40 1 Claim ABSTRACT OF THE DISCLOSURE A self-clearing Weed cutting semisubmerged propeller and cutter blade arrangement combined with a boat havmg shallow draft and for use in vegetation infested waters.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties therein or therefor.

Background of the invention This invention relates to a semisubmerged propeller having self-clearing capabilities and further comprises a fixed cutter blade mounted on the transom of a boat and extending aft on the longitudinal axis, to a position closely adjacent to and in conformation with the leading edges of a semisubmerged propeller. Heretofore operation in swamp conditions where vegetation grows through the water and is considerably high above surface, the only effective vehicle has been an air-propelled swamp boat. These boats are characterized by having a hull generally in the shape of a pram and are propelled by an aircraft engine and propeller of a pusher design. These boats are quite noisy, their efficiency is quite low, and they are not generally suitable for military purposes.

The problem of propeller entanglement with weeds below the surface of the water has been handled in the past by providing the boat with a cutter blade or fin closely adjacent to the leading edges of the propeller. The propeller used is generally affixed to an outboard motor, or to a conventional inboard motor and shaft arrangement wherein the shaft protrudes angularly from the bottom of the boat and terminates at a stern post near the stern much below the surface of the water. These prior arrangements, therefore, provide completely submerged propeller systems which require a considerable draft. Draft may be defined as a distance between the surface of the water to the furthest protruding portion of the boat. While these attempts at self-clearing propellers may be satisfactory in weed cutting action, due to the rather deep draft of the vessel, operation in swamps and in areas where the water is not more than one-half to one foot deep is not possible.

Summary This invention substantially solves the aforementioned problems by providing a substitute for the air-propelled swamp boat but which is more efiicient and produces far less noise, making it suitable for military operations. In the present invention, the propeller shaft emerges from the boat substantially parallel to the boats bottom and the surface of the water with its axis at the waterline. The propeller is of the semisubmerged type that is, only the lower half of the propeller blade circle is below the surface of the water resulting in a draft of perhaps 6 inches to one foot. A Weed cutting blade is affixed to the transom of the boat, the cutting edge of which is positioned closely adjacent to the leading edges of the propeller blades and in conformity therewith. Only minimum clearance need be given between the edge of the cutting blade and the propeller to allow free motion of the propeller but yet provide shearing and cutting action to any weeds which may entangle the propeller above or below the surface of the water.

The obvious advantage of this system is that these boats may operate in shallow swamps heavily infested with vegetation.

Accordingly, it is the principal object of this invention to provide a hydraulic propeller propulsion system capable of operating in shallow, vegetation infested waters.

Another object of this invention is to provide a propulsion system for swamp boats which is highly efiicient and quiet in operation.

Other objects and features of the invention will become apparent to those skilled in the art upon reference to the conveying specifications, claim, and drawings in which:

Brief description of the drawings FIG. 1 is a side elevation showing the configuration of the boat;

FIG. 2 is a detailed elevation view of a boat showing the after portion including the transom, a conforming weed cutting blade and the propeller; and

FIG. 3 is a vertical plan view in the sections showing the details of the semisubmerged propeller and the conforming weed cutting blade.

Description of the preferred embodiment Referring now to FIGS. 1 and 2 there is shown a boat 10 on which is mounted a propeller 12 and a weed cutting blade 14 according to this invention. The boat 10 preferably will have a fiat bottom, and will be of shallow draft. The waterline 16 is drawn on the hull 18 in a position which will be assumed during operation of the boat 10, that is, with the waterline 16 passing as close as possible through the axis of rotation of the propeller, therefor making the propeller a semisubmerged type. A short fin or skeg 20 may be provided along the after portion of the keel of hull 18 to protect the propeller from hitting hard objects.

More particularly, in a semisubmerged propeller design, the propeller shaft is substantially parallel to the longitudinal axis of the boat 10. Attached at the after end of the propeller shaft 22 is a propeller 12 having a hub 26 and blades 24. The forward side of the hub 26 is located a short distance aft of the transom 28 of hull 18.

As more clearly shown in FIG. 2, the cutter blade 14 provided with a relatively narrow section 30 which fills the space between the hub 26 and the transom 28. The after portion of the segment 30 forms a bearing surface for the forward side of the hub 26. Proceeding from the lower section 30, the after edge of the Weed cutter conforms to the hub at point 32 and continues to conform with the propeller blade along the line 34 to a point 36 at the tip of the propeller blade 24.

Referring now to FIG. 3, which is a section along the line 33 of FIG. 2, the cross-section of the weed cutter blade 14 is shown in cross section approximately half way up the length of the propeller blade 24. The leading edges of the propeller blades at 24 pass in close proximity to the weed cutting edge 34 of weed cutter 14. To prevent the blade 24 from striking the cutter 14, as the blade deflects forwardly due to the pressure on its face when propelling the boat through the water, the edge of the cutter blade is chamfered at 40 to provide a ramp surface on the port side in the case of a right handed or clockwise rotating propeller. In the case of a left hand or counterclockwise rotating propeller the chamfered ramp 40 would be provided on the starboard side of the weed cutter 14. Therefore if the blade 24 does deflect 3 forwardly due to the thrust reaction forces, the leading edges of the blade 24 will climb up the ramp 40 without sharply striking the weed cutter 14. The weed cutting blade 14 is attached in any conventional manner to the transom 28 of the boat such as for example by through-bolts 38.

Description of the operation The boat according to this invention may be operated in the swamp lands where the water is extremely shallow and is vegetation infested. The propeller 24 may encounter weeds which will tend to entangle themselves about the blade 24 and tend to entwine about the hub 26. During the upswing of a blade 24, the weeds will be carried with the blade until they encounter the weed cutter 14. The cutting edge 34 which, as previously described, conforms to the leading edge of the blade 24 and is in such close proximity that entangled weeds will be cut and sheared between the leading edge of the propeller blade 24 and the cutting edge 34. The tendency of weeds to entwine themselves about the hub and shaft will also be precluded by the fact that the weed cutter 14 conforms to the hub and shaft at point 32 and 30 respectively so that these weeds also will be cut away from upon rotation of the propeller.

The propeller 24 producing thrust upon the buoyant medium for forward motion, will produce a reaction for which will cause the propeller shaft 22 to be moved forward closer to the transom of the boat. If the propeller shaft were permitted to move closer to the transom, the blades 24 would strike the side of cutter 14. To preclude this tendency of shaft movement, the cutter blade 14 is provided with a small lower portion 30 which provides a given distance between the transom and the forward side of the hub 26 as well as a bearing surface upon which the forward side of the hub 26 may ride. Blade deflection also results from thrust reaction and causes the propeller blades to move in a forward direction closer to the transom of the boat. The cutter blade 14 is chamfered to provide a ramp 40 so the leading edges of the blades 24 will not sharply strike the side of cutter 14 which condition would damage the blades. To prevent the propeller striking hard objects, a fin or skeg is provided to lift the boat 10 and consequently its propeller 24, over any submerged hard object.

As can be seen, there is provided an elficient vehicle using water propulsion which may operate in very shallow weed-infested waters.

It should be understood of course, that the foregoing disclosure relates to only the preferred embodiment of this invention and that numerous modifications or alterations may be made therein such as elimination of the fin or skeg without departing from the spirit and the scope of the invention.

What is claimed is:

1. In combination with a surface watercraft of such extremely shallow draft that a fully submerged propeller is unsuitable, a propeller thruster unit comprising:

a propeller shaft extending aft of the transom of the watercraft, the axis of said shaft being essentially in the plane of the waterline when the watercraft is at rest in the water; semisubmerged screw propeller mounted on a hub located at the end of said shaft, the path of the propeller blades thus being such that the blades are essentially fully above the waterline during one-half their rotative cycle;

a shearing element comprising a vertically oriented block mounted on the transom of the watercraft above the waterline and having an aftward facing surface of width substantially greater than that of the leading edges of the propeller blades in close proximity to and complementary with the side elevation configuration of said shaft and screw propeller for coacting with the propeller blades to cut weeds and the like;

said shearing element having a chamfered face converging toward the portion of the shearing element in closest proximity to the propeller blades; and

an object deflecting skeg mounted forwardly of said propeller on the bottom of said craft.

References Cited UNITED STATES PATENTS 911,939 2/1909 Casaday 114-40 FOREIGN PATENTS 749,945 5/ 193 3 France.

ANDREW H. FARRELL, Primary Examiner 

